This invention relates to the achievement of low cost and versatile electroluminescent lamp products.
As is known by those in the art, an electroluminescent lamp is a surface-area light source consisting of a suitable phosphor placed between electrodes, one of which is essentially transparent. When an alternating current is applied between the electrodes the phosphor emits light, the color of the light dependent on the choice of phosphor.
Such lamps are suitable for a wide variety of applications, including illuminated instrument panels, dial indicators, signs and the like. Such electroluminescent lamp panels can be fabricated by applying a general coating of conductive material, such as indium tin oxide, over the entire substrate panel, the coating providing the material for one of the electrodes, upon which the phosphor and rear electrode layers are applied. In many applications, the full surface of the panel is not required to be light emitting and the unlit portion is masked by printing an opaque ink on the front surface of the lamp. Alternatively, as described in U.S. Pat. No. 4,904,901, material (indium tin oxide) corresponding to the transparent layer is deposited over an entire surface of the panel and is thereafter removed from most of the surface with an acid etch leaving behind areas corresponding to discrete areas of illumination. The phosphor and rear electrode layers are then deposited over the discrete areas. Likewise, either the phosphor or the rear electrode can be applied over desired areas using techniques well known in the art.
According to the invention, for forming a modular lamp unit, flat-form flexible electroluminescent lamps of selected limited size are placed and secured upon a larger printed circuit substrate employing surface mount techniques. The substrate and secured lamps can be subsequently deformed into a desired shape or incorporated as is into a product. Alternatively, the lamp and the substrate may be subject to separate preforming operations and can then be joined together. In all these cases, the area occupied by the lamp is restricted solely to the area desired to be illuminated. Thus, the invention reduces production cost by significantly reducing the area covered by the lamp. As is known in the art, conductive materials (e.g. indium tin oxide) used to provide an electrode of the lamp can be relatively expensive. Further, smaller segmented and individually addressable lamps consume less electrical power, generate less heat and are more reliable than large full area lamps having opaque patterns over unlit portions of the lamp. Opaque patterns for covering lit line traces between desired areas of illumination are also eliminated. Automation of the process for placing and securing individual lamps is preferably achieved by programmed pick and place robots for selecting and placing the lamp on the surface of a receiving printed circuit substrate according to pre-specified instructions, followed by automated steps to connect and secure the lamps to the substrate.
Shaping the lamps and substrate permits their use in a wide variety of applications, e.g., to accommodate special aesthetic designs or where space is limited. In addition, the flexible nature of the lamps and use of a flexible substrate permit their use in applications where the flexible substrate is actuated, such as in the opening and closing of a cassette player door. Novel thermalforming techniques enable molding of a preformed lamp member into a stable desired three-dimension shape without impairing the function of the lamp.
The invention also permits a number of lamps to be provided onto a printed circuit substrate, each lamp or separate groups being independently addressable and having different colors or brightness characteristics. Individually addressable lamps of the unit may be individually driven or may be powered by a single power supply.
In one aspect of the invention a method for forming an electroluminescent lamp includes the following steps. A multi-layer sheet form electroluminescent lamp is provided. The multi-layer sheet form lamp includes a pair of sheet-form conductive layers, one of which is transparent for transmitting light emitted from the particles, an electroluminescent sheet-form layer disposed between the pair of sheet-form conductive layers and having electroluminescent particles, and a carrier substrate for supporting the pair of sheet-form conductive layers and electroluminescent sheet-form layer. The multi-layer sheet form lamp is heated at a temperature sufficient for maintaining the operational integrity of the carrier substrate and the thermoplastic layers. The multi-layer sheet form lamp is then formed into a desired three-dimensional shape.
In another aspect, the invention provides a three-dimensional illuminating object including forming a lamp member with the following steps. A generally sheet-form biaxially oriented light-transmitting polyester carrier substrate is provided upon an electroluminescent lamp. The electroluminescent lamp includes a thin film transparent electrode deposited on the carrier substrate and a plurality of intimately bonded superposed polyvinylidene fluoride layers including a layer containing phosphor particles, a layer containing insulative particles and a layer containing conductive particles forming a back conductive electrode. The lamp member is heated to a molding temperature in the range between 190xc2x0 F. and 270xc2x0 F. and molding the heated lamp member at the temperature to a desired three dimensional shape whereby shrinkage of the carrier substrate is avoided and the operational integrity of the polyester carrier substrate and the polyvinylidene layers is maintained. The lamp member is then cooled in the three-dimensional molded form
In another aspect, a method of constructing a three dimensional illuminating object includes forming a lamp member by providing upon a generally sheet-form, light-transmitting thermoplastic carrier substrate an electroluminescent lamp including a thin film transparent electrode deposited on the carrier substrate and, thereon, intimately bonded superposed thermoplastic layers having a layer containing phosphor particles that forms a phosphor layer, an insulative layer and a back conductive electrode layer. The lamp member is placed over a die of desired three-dimensional shape. The lamp member is then pressure formed by pressing the lamp member against the die to form the lamp member to the desired three-dimensional shape under conditions maintaining the operational integrity of the carrier substrate and the thermoplastic layers to produce a formed shape capable of emitting light.
Embodiments of these aspects of the invention may include one or more of the following features.
The heating step includes heating the multi-layer, sheet-form electroluminescent lamp in a temperature range below the softening point temperature of the carrier substrate, e.g., in a temperature range between 190xc2x0 F. and 270xc2x0 F., and preferably in a range between 230xc2x0 F. and 260xc2x0 F. At least one of the conductive layers includes a fluoropolymer resin.
The forming step includes applying pressure after heating of the multi-layer, sheet-form electroluminescent lamp. In one embodiment of the invention, the method includes the steps of providing a die having a male member and a mating female member, which together define the desired three-dimensional shape; heating at least one of the male member and female member of the die; positioning the multi-layer, sheet-form electroluminescent lamp between the male member and female member of the die; and applying pressure to the male member and female member of the die. A clamp is used to apply the pressure to the male and female members.
Where multiple lamps are employed, a first one of the electroluminescent lamps has a light-emitting characteristic (e.g. color, intensity) that is different than a light-emitting characteristic of a second one of the electroluminescent lamps.
The multi-layer, sheet-form electroluminescent lamp includes contact conductors, which may be deformed to provide spring detents. In some embodiments, the conductors are deformed in a direction opposite to that of another of the conductors.
In constructing a three dimensional illuminating object including a formed lamp member, the carrier substrate is a biaxially oriented sheet and may be a polyester including any of a variety of polymers or a polycarbonate material. The thermoplastic layers include polyvinylidene fluoride, fluoropolymer vinyl, polyester, polyimide or other thermoplastic resins. Prior to pressure forming the lamp member, the lamp member is heated to a molding temperature below the softening point temperatures of the thermoplastic of the carrier substrate and of the thermoplastic resins of the superposed layers and, thereafter, the lamp member is cooled in the molded three-dimensional form. The molding temperature is below a temperature at which substantial shrinking of the carrier substrate occurs. The molding temperature is in the range between 190xc2x0 F. and 270xc2x0 F. and is preferably between 230xc2x0 F. and 260xc2x0 F.
The three dimensional illuminating object can be in the form of a decorative embossed, self-illuminating figure or alphanumeric symbol. Alternatively, the three dimensional illuminating object can be in the form of a shaped pendant self-illuminating ornament or identifying logo.
In general, the achievement of a single overall lamp module that is practical and inexpensive to manufacture, and which selectively emits various qualities of light at freely selectable locations is a particularly important practical achievement of the present invention. Another important achievement is the practical achievement of three-dimensional electroluminescent lamps and structures carrying such lamps.
Other advantages and features of the invention will become apparent from the following description and from the claims.